Add a system for registering function pointers similar to registering queries

[oli-obk]

Proposal

We have some queries, that should not be queries, but only are queries, because their body needs to live in a crate other than rustc_middle. Queries are overkill for this and have various problems if the arguments are not incremental/query-cache safe (see rust-lang/rust#115819). Instead I propose to add a way to add function pointers to Providers that will then get stored in TyCtxt and have a method generated on the TyCtxt that invokes the function pointer.

Mentors or Reviewers

The implementation should be fairly straight forward, so anyone from T-compiler or T-compiler-contributors

Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

cc @rust-lang/compiler @rust-lang/compiler-contributors

[lcnr]

😁 there is already the accepted MCP #395 which is pretty much exactly equal but has never been implemented. I guess given that it has been more than 2.5 years

@rustbot second

[RalfJung]

So, the 10-day period is already over then, since it started 2.5 years ago? ;)

[apiraino]

I would close as "duplicate" (if such a label makes sense)